Views: 0 Author: Fenhar Publish Time: 2026-07-23 Origin: Site
G11 is a high-pressure thermoset laminate made from woven glass cloth bonded with a specially formulated high-temperature epoxy resin system. The glass reinforcement provides mechanical strength and dimensional stability, while the modified resin matrix gives G11 its defining characteristic: the ability to retain structural integrity and mechanical properties at temperatures that would soften or degrade standard epoxy laminates.
Under NEMA (National Electrical Manufacturers Association) classification, G11 is designated under LI-1 Grade G-11. It also carries international equivalents: IEC 60893 EP GC 203 and military specification MIL-I-24768/3 Type GEB. These standards ensure consistency in manufacturing and performance across suppliers.
The material is supplied as flat sheets in standard mill sizes, typically ranging from 0.2 mm to 100 mm in thickness. It is also available in rod and tube forms for specialized applications.
What sets G11 apart from other glass-epoxy laminates is its resin chemistry. The epoxy system used in G11 is crosslinked to a higher degree than standard epoxy formulations. This increased crosslink density raises the glass transition temperature (Tg) and improves the material's resistance to thermal degradation. The result is a laminate that maintains its mechanical strength and electrical insulating properties across a broader temperature range—from cryogenic conditions up to continuous service at 150–175°C.
G11 is also halogen-free and non-brominated. Unlike FR4, which achieves flame retardancy through brominated additives, G11 does not contain these compounds. This makes it a preferred choice in applications where halogen-free materials are specified, particularly in rotating electrical equipment where bromine compounds can contribute to chemical attack on metal components.
Engineers choosing between G10, FR4, and G11 need to understand that these materials share a common foundation—woven glass fabric in an epoxy matrix—but diverge significantly in their thermal performance and flame-retardant characteristics.
The table below summarizes the key distinctions:
The most meaningful difference is thermal performance. G10 and FR4 are suitable for general-purpose applications up to roughly 130°C. G11, by contrast, is engineered for sustained operation at 150°C and above. This is not a marginal improvement—it represents a different class of material altogether.
For applications that require both high-temperature performance and flame retardancy, G11 is not the right choice. That combination is served by FR5, which is the flame-retardant counterpart to G11. FR5 uses the same high-temperature epoxy resin system as G11 but incorporates brominated additives to achieve a V-0 flammability rating.
G11 delivers robust mechanical performance across a wide temperature range. The glass cloth reinforcement provides anisotropy—meaning properties differ between the lengthwise (warp) and crosswise (fill) directions relative to the weave. Designers should account for this when orienting parts for specific load paths.
Tensile Strength (ASTM D638):
Lengthwise: ~40,000–48,000 psi (275–330 MPa)
Crosswise: ~40,000–44,000 psi (275–303 MPa)
Flexural Strength (ASTM D790):
At room temperature: ~54,000–75,000 psi (372–517 MPa)
At 150°C: Retains a minimum of 50% of room-temperature value
Compressive Strength (ASTM D695, flatwise): ~50,000–68,000 psi (344–469 MPa)
Impact Strength (Izod, edgewise): ~9.5–10.0 ft-lb/in
Rockwell Hardness (M Scale): 110–115
The defining mechanical feature of G11 is its strength retention at elevated temperature. While most epoxy laminates lose a substantial portion of their flexural strength as they approach their glass transition temperature, G11 is specifically formulated to maintain at least half of its room-temperature flexural strength at 150°C. Some formulations guarantee a Tg of 180°C or higher.
This characteristic is not merely a laboratory curiosity—it translates directly to real-world reliability. In applications like generator slot wedges, motor support structures, and high-temperature insulating components, G11 continues to bear mechanical loads at temperatures where G10 or FR4 would soften and lose their load-carrying capacity.
G11's thermal performance is its primary differentiator. The material is rated for continuous operation at temperatures that would compromise standard epoxy laminates.
Continuous Service Temperature: 150–175°C, depending on formulation and specific application conditions. Some high-performance grades extend this to 180°C.
Glass Transition Temperature (Tg): 155–190°C. The Tg marks the temperature at which the polymer matrix transitions from a rigid, glassy state to a more rubbery state. G11's high Tg ensures that the material maintains its mechanical stiffness and dimensional stability well into the elevated-temperature range.
Temperature Index: 180°C (mechanical) / 160–170°C (electrical). The temperature index is a standardized measure of a material's long-term thermal endurance, indicating the temperature at which the material can operate continuously for an extended period without losing 50% of a specified property.
Coefficient of Thermal Expansion (CTE): Approximately 9.0 × 10⁻⁶ cm/cm/°C, with crosswise CTE around 0.83 × 10⁻⁵ in/in/°F. The relatively low and stable CTE contributes to G11's dimensional stability under thermal cycling.
Thermal Conductivity: Low, consistent with other glass-reinforced epoxy laminates. This makes G11 an effective thermal insulator—useful in applications where heat containment or isolation is desired, but a consideration when the part must dissipate heat.
For context, G10 typically supports continuous service up to the low 130°C range, while FR4 standard grades are rated around 120°C, with high-Tg FR4 variants reaching 150–180°C. G11's thermal capability sits at the upper end of this family of materials.
G11 is an effective electrical insulator across a broad range of temperatures and humidity conditions. Its electrical properties remain stable even when the material is exposed to elevated temperatures or moist environments.
Dielectric Strength: 16–18 kV/mm (perpendicular to lamination), with some grades reaching 550 volts/mil. Dielectric strength is thickness-dependent, and values should be verified with the supplier for the specific thickness and test conditions under consideration.
Dielectric Constant (at 1 MHz): ~4.2–4.7
Dissipation Factor (at 1 MHz): ~0.015–0.020
Volume Resistivity: ~5.0 × 10⊃1;⊃2; Ω·cm
Arc Resistance: 120–185 seconds
G11 maintains good dielectric properties even under humid conditions. This is partly attributable to its low moisture absorption—water uptake can degrade electrical insulation performance, and G11's low absorption helps preserve its dielectric strength and surface resistivity in wet or high-humidity environments.
The material's electrical performance is also stable across frequency. While dielectric constant and dissipation factor are frequency-dependent—as with any dielectric material—G11 exhibits consistent behavior over a useful range of frequencies.
Density (Specific Gravity): 1.80–1.95 g/cm³
Water Absorption (24 hours, ASTM D570): 0.05–0.15%
Color: Typically available in natural (translucent yellow-green), black, or custom colors
G11's low moisture absorption is a significant practical advantage. In humid environments or applications where the material is exposed to oils, coolants, or aqueous solutions, G11 maintains its dimensional stability and electrical properties more effectively than materials with higher water uptake.
The material resists oils, hydrocarbons, and mild acids and alkalis. As with other epoxy-based laminates, aggressive oxidizing agents and certain solvents can attack the resin matrix. For outdoor exposure, UV degradation is a consideration—prolonged sunlight can break down the epoxy surface, and protective coatings or surface treatments are recommended for long-term weathering exposure.
G11 is specified in applications where the combination of high-temperature capability, mechanical strength, and electrical insulation is required. Typical uses include:
Power Generation Equipment: Generator slot wedges, stator and rotor coil support structures, and insulating components in high-voltage motors. G11's ability to maintain mechanical strength at elevated temperatures is critical in these applications, where the material must withstand both thermal stress from the windings and mechanical stress from rotational forces.
Electrical Insulation: Switchgear insulating components, bus bar insulators, terminal blocks, and flange isolation gaskets. G11 provides reliable electrical isolation in high-voltage environments where heat buildup is a concern.
High-Temperature Structural Components: Support pads, spacers, washers, and machined parts exposed to sustained heat. The material's creep resistance and dimensional stability under load at elevated temperatures make it suitable for structural applications where other plastics would deform.
Transportation: Insulating structural components in rail vehicles and electric vehicle powertrains, where thermal management and electrical safety are both priorities.
Aerospace and Defense: Antenna insulators and other components requiring high reliability under thermal and mechanical stress.
G11 machines similarly to G10 and FR4, but the glass reinforcement makes it abrasive to cutting edges. Following good practices will produce clean, accurate parts while extending tool life:
Tooling: Use sharp carbide or diamond tooling. High-speed steel tools will wear rapidly and should be avoided.
Feed Rates and Speeds: Moderate feed rates and steady cutting speeds. Avoid excessive feed rates that can cause edge fraying or delamination.
Drilling: Use backing support to prevent breakout on the exit side. Peck drilling helps clear chips in deep holes. For holes with critical tolerances, consider drilling undersize and reaming to final dimension.
Dust Control: Glass fiber dust is a respiratory hazard. Use effective dust extraction and wear appropriate respiratory protection.
Surface Preparation: Light abrasion followed by solvent cleaning improves adhesive bonding performance.
When specifying G11, reference the relevant standards to ensure material conformance:
NEMA: LI-1 Grade G-11
IEC: 60893 EP GC 203
Military: MIL-I-24768/3 Type GEB
DIN: Hgw 2372.4
Flammability: UL 94 HB (non-flame-retardant)
Note that G11 is not a flame-retardant grade. If your application requires a V-0 flammability rating in addition to high-temperature performance, specify FR5 instead.
Choose G11 when your application demands:
Sustained operation above 130°C — if your continuous service temperature exceeds the capability of G10 or standard FR4, G11 is the logical upgrade
Mechanical load-bearing at elevated temperature — if the part must support structural loads while hot, G11's strength retention is critical
Electrical insulation in hot environments — if the insulating component is exposed to heat from nearby windings, bus bars, or ambient conditions
Halogen-free material — if brominated flame retardants are prohibited or undesirable
Low moisture absorption — if the material will be exposed to humid conditions or liquids
For applications requiring flame retardancy, choose FR4 for standard temperatures or FR5 for high temperatures. For general-purpose applications without extreme thermal demands, G10 remains a cost-effective option.
